1. Field of the Invention
The present invention relates to bottled water (preferably refrigerated) dispensers, and more particularly to an improved bottled water dispenser for dispensing water that has been sanitized using ozone and more particularly to an improved method and apparatus for sanitizing water that is to be dispensed from a water cooler of the type having a cabinet with one or more spigots that are manually operable to dispense water from a reservoir water supply that is hidden inside the cabinet, and wherein air diffusers of improved configuration are disclosed that can be used to diffuse air into the reservoir.
2. General Background of the Invention
There are several types of cabinet type water dispensers in use today. One of the most common types of such water dispensers is a floor standing cabinet having an open top that receives a large inverted bottle. The bottle is typically of a plastic or glass material having a constricted neck. The bottle is turned upside down and placed on the top of the cabinet with the neck of the bottle extending into a water filled reservoir so that the water seeks its own level in the reservoir during use. As a user draws water from a spigot dispenser, the liquid level in the reservoir drops until it falls below the neck of the bottle at which time water flows from the bottle and bubbles enter the bottle until pressure has equalized. Inverted bottle type water dispensers are sold by a number of companies in the United States and elsewhere. Many are refrigerated.
Other types of water dispensers have an outer cabinet that contains a reservoir or water supply. These other types of water dispensers having a cabinet include one type that stores a large bottle (such as three or five gallon) at the bottom of the cabinet. A pump transfers water from the large bottle to the reservoir. At the reservoir, the water is typically refrigerated.
Another type of water dispenser simply connects a water supply (eg. city water, well water) directly to a reservoir that is hidden inside the cabinet. A float valve or other water level controller can be provided to insure that the reservoir is always filled with water but does not overflow. Water that is transferred from city water, well water or another source can be filtered or otherwise treated before being transmitted to the reservoir.
All of these types of water dispensers that employ cabinets typically have one or more water dispensing spigots on the outside of the cabinet. These spigots are typically manually operated, but can be automatically operated. For example, water vending machines dispense after a consumer pays for water. The water is automatically dispensed when coins are fed to the machine.
One of the problems with cabinet style water dispensers is that of cleansing the reservoir from time to time. Because the reservoir is not air tight, it breathes so that bacteria can easily enter the reservoir over a period of time. The reservoirs are typically contained within the confines of the cabinet and are not easily accessed and cleaned by consumers or end users.
For inverted bottle type dispensers, in addition to the problem of an open top, the five gallon bottles are themselves a source of bacteria and germs. Most of these bottles are transported on trucks where the bottles are exposed to outside air. They are handled by operators that typically grab the bottle at the neck, the very part of the bottle that communicates with the open reservoir during use. Unfortunately, it is difficult to convince every person that handles these bottles to wash their hands frequently enough.
In order to properly sanitize such a water dispenser or cooler, the user must carefully clean the neck of the bottle prior to combining the bottle with the cabinet. Further, the user should drain and sanitize the reservoir from time to time. The cleansing of the reservoir in such a water dispenser is a time consuming project that is typically not performed at regular intervals.
The dispensing spigots that are provided on common cabinet type water dispensers can also be a source of contamination. These spigots are typically manually operated and are therefore a source of contamination from the users that operate them. Very small children have also been known to drink directly from the spigot, probably because the spigot is located at a distance above the ground that closely matches the elevation of a child's mouth at an early age. Therefore, sanitation of the spigots as well as the reservoir should be a part of routine maintenance.
Process ozone diffusion by bubble reactor method in small static volumes of water with abbreviated water columns to diffused ozone levels satisfactory to disinfect microorganisms in brief time periods can be difficult to achieve. The chief hurdle involved is ozone diffusion contact surface area and time. The present invention is directed to an economical means of overcoming each of the factors that limit process ozone's potential disinfecting capacity. It is concerned with the optimization of each point in small automated ozonation systems both upstream and downstream from the ozonator. The object of this effort is to devise a single, economical, high longevity system capable of sanitizing all of the shapes and sizes of water dispensers in use today.
Until recently, the ozone water and related equipment sanitization and disinfection industry has been geared to large scale commercial, industrial and municipal applications not under space or equipment cost restraint. However, a growing demand for suitable sized ozone equipment with economy of scale for addressing less demanding, small sanitization and disinfection applications like water dispenser device sanitization has surfaced.
The chief difference between small and large applications is small applications are typically concerned with ozonating small, fixed, static volumes of water over adjustable dwell time intervals until adequate levels of disinfection or sanitization are achieved as opposed to large applications ozonation of continuously exchanged, large water volumes. The lowered number of variables offered by reduced temperature, static water volumes ozonated over time is the only built-in advantage available to small applications. During the process of re-engineering equipment and reducing costs to fit small application needs, it was found that beyond basic principles, much of the available industrial technology proved of limited value.
Attempts at using prior art to address small applications have resulted in either failure to achieve minimal levels of sanitization or where success was achieved, systems that could not remain cost competitive.
A number of factors influencing ozone diffusion into water by bubble reactor methods and their technical limitations related to small applications follows. Due to cost and space constraints small applications are limited to the use of small ambient air fed ozonators capable of generating less than 1% by weight ozone. This is contrasted by large scale applications' use of chilled LOX fed ozonators capable of generating up to 12% ozone by weight. Ozone is much more soluble in cold water than room temperature or warm water. A particular small application has little control over this factor. The water dispenser application is fortunate in the sense that average water temperatures are in an optimal 4-8 degree Celsius range. A large hurdle for small applications exhibiting static water volumes with a short (i.e., a few inches) water column is the ozone to water contact time. Bubble reactors usually vent more process ozone than they diffuse. The available options are longer dwell times, reduced airflow and smaller bubble size. Compare an average water dispenser's 1-3 liter volume, 4-6 inch water columns (0.15-0.21 psi back pressure), and 0.5-2 second bubble contact time at 1% ozone concentration with a large scale operation's 16-20 inches, 6-8.5 psi column's 15-20 second contact time with 12% ozone by weight. Since small systems are chiefly intermittent, auto-cyclic, programmable devices, this factor can be optimized by critical dwell time control and use of variable output ozonators for controlling both cycle width and ozone concentration tailored to water species, water volume and column height. Additional optimization is achieved by diffuser material choice and controlled airflow. Since small systems are chiefly scheduled for use in inside environments, over ozonation, using too high an ozone concentration and venting of surplus process ozone to air raises an air quality concern. It is imperative that small applications optimization addresses this potential health hazard. Small water dispenser applications (especially those using inverted water bottle) cannot blow large volumes of ozonated air into a small open systems bubble reactor reservoir containing a small volumes of water without either causing air displacement flooding of the reservoir or producing a substantial vapor phase that vents most of the water from the reservoir and reserve by evaporation. An additional difficulty is the loss of minimal head pressure, production of a large bubble with inadequate surface contact area resulting in a near total systems loss of process ozone. These factors are subject to optimization and are key to small applications success. Though large applications address flow control through fine bubble diffusers, its use is confined to high ozone concentration feed gas, fed through a high volume of fine bubble diffusers primarily for oxidation of bio-solids in moving volumes of water where bubble retention time is not critical. The data does not deal with potable water disinfection or sanitization parameters. Consequently the data on diffused gas to water and diffuser area to water volume ratios do not apply to low ozone concentration, time dependent small systems potable water sanitization.
Diffuser materials producing smaller bubbles per unit ozonated air volume exhibit a much greater surface area than like volumes of large bubbles. The higher the surface area, the greater the contact diffusion. Within limits, this factor can be optimized and is one of the main keys to successful small applications.
Internal Bubble Pressure: Small bubbles produced by fine bubble diffusers exhibit higher internal bubble pressures, hence greater diffusion by pressure/temperature relationship. In addition, their greater pressure retards their rise velocity, thus increasing contact and pressure/temperature diffusion time and affords higher structural integrity making them less subject to expansion and coalescence. This factor is optimized by diffuser material choice and control of airflow and is another key to successful small applications.
While prior patents have addressed water dispenser ozonators in general, various component, the present invention provides the means for optimization of ozone diffusion utilizing unique airflow control and diffuser technology. The purpose behind optimizing airflow is primarily twofold: first, to increase air dwell time across a cold plasma coronal discharge tube to increase ozone concentration and second, to reduce the large bubble fraction generated at the surface of a diffuser. The generation of small bubble sizes in gas diffusion bubble reaction chambers in order to increase surface area and contact time has long been an industry dream. However, the lack of need generated by past engineering success has caused industry to stop short of original goals.
Diffuser manufacturers have engineered small pore size, low permeable diffusers that in some cases require greater pump pressures for flow initiation. Higher pressure materials are not optimal for small low pressure/volume open systems applications as they decrease pump life and often do not supply an adequate volume of small bubbles for ozonation. Quite often, they are more subject to pore plugging than lower initial bubble pressure materials. The author's testing indicates that different manufacturer processing techniques for a single given media exhibiting identical mean particle and resulting pore size generate large variations in a diffuser's initial bubble pressure where at lowered IBPs, a diffuser will not only produce like sized bubbles, but a greater quantity of bubbles for less work. As a rule, the lower internal bubble pressure per same material and parameter diffuser will exhibit a greater spacing between active surface pore channels. Additionally, the less flow restricted material produces higher volumes of like sized bubbles with reduced vertical bubble velocity differentials and turbulence.
These preferred characteristics lead to decreased lateral and vertical bubble coalescing, reduced bubble expansion and rise rates, hence higher diffusion efficiency. Lower initial bubble pressure materials require a greater wall thickness and surface area to match the performance of higher initial bubble pressure materials. Otherwise, bubble size will increase to non-optimal proportions.
Conditions for minimal adverse bubble reactions in specific mean pore diameter/internal bubble pressure diffuser material producing specific bubble sizes at 0.05-1 liter/minute flow volumes in water columns ranging from 1-50 inch heights, include active pore spacings equaling thrice the bubble diameter both laterally and vertically at the diffuser surface where mean pore to bubble diameter ratio ranges from about 1:12.5 to 1:50. Application of these ratios to media diffuser surface area is tied to performance test treatment studies involving given water volumes and column heights, independently varying airflow rates at known ozone concentrations, and noting bubble size and bubble population size with respect to dissolved ozone concentration over a given time interval.
Once transfer efficiencies are determined for each situation, variable diffuser surface area tests noting bubble size and bubble population are performed and transfer efficiencies determined. By comparing the various flow and time varying studies against diffuser area studies and comparing bubble sizes and populations, one arrives at the optimal diffuser material surface area, flow rate and dwell time.
Prior art for commercial and industrial sized applications represents a balance between bubble size and bubble volume. Industry experience has been negatively influenced by misapplication of fine pore size diffusers to high solids and TDS fluids that promote rapid pore plugging, experience that crossed over to low mineral and solids water species like potable water disinfection. Furthermore, large commercial and industrial applications could not afford downtime on dynamic systems that operate 24 hours a day.
The use of very fine pore size diffusers application was largely abandoned by wastewater and potable water treatment out of past reservations and lack of research data for generating optimally engineered materials. To date, the recent interest in small applications has not triggered mainstream development of new diffuser materials/geometry innovations.
Although diffuser manufacturers typically produce fine pore diffusers to relatively homogeneous mean pore size standards, large pore sizes that channel high air volumes away from the smaller interconnected pore diameters occur in virtually every material tested. This is often complicated by an inability to effectively seal off material connection air leaks. Testing revealed that high permeability channel flows are the first to terminate large bubble production when airflow rates are reduced. This adjustment allows existing diffusers to operate at near rated design capacity and will serve as a stopgap measure until better solutions emerge. The optimal diffuser-airflow balance of small bubbles with reduced large bubble fraction displaying adequate remaining small bubble volumes suitable for ozonation occurs at approximately 50% of open flow rate on average for any given diffuser and water column height. This air volume reduction approximately equals the large gas bubble volume displaying poor diffusion characteristics.
The present invention thus provides an improved self sanitizing water dispenser apparatus as well as a method for generating ozone for cleaning the reservoir and the water contained within it.